1. Field of the Invention
The present invention relates to novel polymeric compositions and more particularly to contact lenses made therefrom. The invention further particularly relates to polysiloxane-containing monomers having at least one polar fluorinated side chain. The monomers described herein can be used to make "hard" or "soft" contact lenses, intraocular implants, as well as other prostheses, and more particularly "soft" hydrogel contact lenses.
2. Background
In the field of contact lenses, various factors must combine to yield a material that has appropriate characteristics. Oxygen permeability, wettability, material strength and stability are but a few of the factors which must be carefully balanced to achieve a useable contact lens. Since the cornea receives its oxygen supply exclusively from contact with the atmosphere, good oxygen permeability is a critical characteristic for any contact lens material. Wettability also is important in that, if the lens is not sufficiently wettable, it does not remain lubricated and therefore cannot be worn comfortably in the eye. The optimum contact lens would therefore, have both excellent oxygen permeability, and excellent tear fluid wettability.
Polysiloxane materials are useful materials for making contact lenses due to, among other properties, their excellent oxygen permeability. See U.S. Pat. Nos. 4,153,641 and 4,189,546. However polysiloxanes are generally hydrophobic. Certain hydrophilic functional groups may be attached to polysiloxane-containing monomers, or prepolymers to improve their wettability. See U.S. Pat. Nos. 4,260,725 and 4,259,467. However, many hydrophilic comonomers are known to be incompatible with the polysiloxane monomers in the monomer mix, and require the presence of solubilizers and compatibilizers for the monomer mix properly polymerize. Without such compatibilizers, the copolymer may not polymerize at all, risking varying degrees of phase separation which renders the polymerized material opaque.
In addition to oxygen permeability, wettability and compatibility requirements, contact lens materials must resist deposits. Some polysiloxane materials tend to accumulate deposits. Fluorinating certain polysiloxanes monomers is known to improve deposit resistance. See, for example U.S. Pat. Nos. 4,440,918, 4,990,382, 4,954,587, 5,079,319 and 5,010,141.
Fluorinated polysiloxanes with useful properties for non-hydrogel contact lenses are disclosed in U.S. Pat. Nos. 4,810,764 and 5,142,009. In further experimentation with these materials, it was determined that a hydrogel having the oxygen permeability advantages imparted by the siloxane group, and the lipid resistance imparted by the fluorinated groups would be particularly advantageous. However, because the fluorinated polysiloxane monomers are difficult to solubilize in the hydrophilic monomers used, it is difficult to make viable hydrogel formulations for contact lenses using this approach. If comonomers are not sufficiently soluble in one another, phase separation will occur rendering the polymerized material opaque. Such a result is not desirable for a material which must be transparent, such as a contact lens.
Compatibilizers or solubilizers such as methyl ethyl ketone (MEK) have been used to get certain fluorinated siloxane-containing monomers into solution to form films or lenses. However, such solubilizers and compatibilizers often affect purity and must be extracted from the resulting polymer. Such extraction requires additional processing steps. Further, if there is a large difference in polarity between the siloxane-containing monomer and the hydrophilic monomer, even the presence of solubilizers such as MEK will not keep the comonomers in solution.
Therefore, a hydrolytically stable polymeric system comprising the benefits of polysiloxane-containing monomers for oxygen permeability and material strength, and fluorinated side-groups for resistance without use of compatibilizers or solubilizers would be of great advantage for a hydrogel formulation.